Time, Gauge, and the Superposition Principle in Quantum Gravity

TL;DR

This paper explores the challenges of defining time in quantum gravity, highlighting ambiguities and interference effects arising from using approximate clocks to interpret observables.

Contribution

It analyzes the implications of time parametrization and superposition in quantum gravity, offering insights into the role of unobservable time and clock degrees of freedom.

Findings

Multiple quantum states can produce identical predictions but interfere due to time ambiguities.

Using approximate clocks introduces superposition effects that impact observable interpretations.

The role of unobservable time complicates the quantization of reparametrization-invariant systems.

Abstract

The quantization of time-reparametrization invariant systems such as general relativity is plagued by an ambiguity relating to the role of time in the theory. If one parametrizes observables by the (unobservable) time, and then relies on the existence of an approximate "clock" degree of freedom to give physical meaning to the observables, one finds multiple quantum states that yield the same predictions yet interfere with each other.